Estimate alcohol
(OG − FG) × 131.25For 1.050 to 1.010, the estimated result is 5.25% ABV.
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Beer ABV Calculator
Enter hydrometer readings from before and after fermentation to estimate alcohol and see how far the beer attenuated.
READ THE RESULT
One gravity change, three useful numbers
ABV estimates alcohol by volume. Apparent attenuation describes the percentage drop in gravity points, while ABW expresses alcohol as a percentage of beverage mass.
Compare gravity points
(50 − 10) ÷ 50 = 80%Alcohol lowers density, so apparent attenuation is not real extract loss.
COMMON QUESTIONS
Beer ABV calculator FAQ
How do I calculate beer ABV from gravity?
Subtract final gravity from original gravity and multiply the difference by 131.25. This common homebrewing equation is an estimate rather than a laboratory alcohol measurement.
What are OG and FG?
Original gravity is measured before fermentation. Final gravity is measured after fermentation has finished. Their difference reflects the change as yeast consumes fermentable extract and produces alcohol.
What is apparent attenuation?
Apparent attenuation is the percentage reduction in gravity points from OG to FG. It is called apparent because alcohol lowers the finished beer’s density.
Can a refractometer reading be used directly after fermentation?
Not without correction. Alcohol changes a refractometer reading, so post-fermentation Brix must be corrected or checked with another appropriate method.
Research-based sources
- UK Government: Alcoholic strength technical guide — gravity-based beer alcohol factors and measurement requirements.
- National Institute of Standards and Technology: Measuring alcohol — hydrometer and laboratory measurement context.
- Heriot-Watt University: Estimating alcohol from brewing data — comparison of gravity-based calculation methods.